rem样板

window.onload=window.onresize=function(){
    var rem=document.documentElement.clientWidth*20/320;
    document.documentElement.style.fontSize = rem+'px';
};

meta标签：

<meta name="viewport"
          content="width=device-width, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0, user-scalable=no">

(function (doc, win) {
  var docEl = doc.documentElement,
    resizeEvt = 'orientationchange' in window ? 'orientationchange' : 'resize',
    recalc = function () {
      var clientWidth = docEl.clientWidth;
      if (!clientWidth) return;
      docEl.style.fontSize = 12 * (clientWidth / 375) + 'px';
    };

  if (!doc.addEventListener) return;
  win.addEventListener(resizeEvt, recalc, false);
  doc.addEventListener('DOMContentLoaded', recalc, false);
})(document, window);